I got onto Symantec and their fix was to
- Settings
- Control Panel
- Security Center
- Click "Virus Protection"
- Click the "Recommendation" button
- Check the box for "I have an antivirus program that I'll monitor myself"
This stops the "Your computer might be at risk" balloon from appearing but it does mean that I have to verify that NAV2009 is up and running every time I start my PC and at regular intervals thereafter!
I guess my days of using Norton for anti-virus software are numbered as it does not appear that they are very good about making sure that their product works with ease!